How many times have you sat down to watch TV or a movie, only to immediately shift your attention to your smartphone or tablet? Known as “media multitasking”, this phenomenon is so common that an estimated 178m US adults regularly use another device while watching TV.

Media multitasking is when people engage with multiple devices or content at the same time. This might be using your smartphone while watching TV, or even listening to music and text messaging friends while playing a video game.

One recent study looked at the body of current research on media multitasking (consisting of 22 peer-reviewed research papers) and found that self-reported “heavy media multitaskers” performed worse on attention and working memory tests. Some even had structural brain differences.

The study found that “heavy” media multitaskers performed about 8-10% worse on sustained attention tests compared to “light” media multitaskers. These tests involved participants paying attention to a certain task (such as spotting a specific letter in a stream of other letters) for 20 minutes or more.

Researchers found that on these tests (and others) the ability to sustain attention was poorer for heavy multitaskers. These findings might explain why some people are heavy multitaskers.

If someone has a poor attention span, they may be likely to switch between activities quickly, instead of staying with just one.

Heavy media multitaskers were also found to perform worse than light media multitaskers on working memory tests. These involved memorising and remembering information (like a phone number) while performing another task (such as searching for a pen and piece of paper to write it down).

Complex working memory is closely linked with having better focus and being able to ignore distractions.

But while researchers have confirmed that heavy media multitaskers have worse memory and attention, they are still uncertain about what causes heavy media multitasking.

Do heavy media multitaskers have worse attention because of their media multitasking? Or do they media multitask because they have poor attention?

It might also be an effect of general intelligence, personality, or something else entirely that causes poor attention and increased media multitasking behaviours.

But the news isn’t all bad for heavy multitaskers. Curiously, this impairment might have some benefit. Research suggests that light media multitaskers are more likely to miss helpful information that isn’t related to the task they’re currently performing.

For example, a person may read with a radio playing in the background. When important breaking news is broadcast, a heavy media multitasker is actually more likely to pick it up than a light media multitasker.